The anterior cruciate ligament is the second largest ligament in the knee. The only ligament structure of greater strength and size is the posterior cruciate ligament. The anterior cruciate ligament and posterior cruciate ligament act in conjunction to provide both static and dynamic stability to the knee function. In the static mode, the anterior cruciate ligament prevents anterior subluxation of the tibia on the femur. In a similar fashion, the posterior cruciate ligament prevents posterior subluxation of the tibia on the femur. When both the anterior cruciate ligament and posterior cruciate ligament are intact, they work in conjunction with the medial collateral ligament, lateral collateral ligament and bony and cartilagenous materials in the knee to prevent varus and valgus deformity.
In a dynamic mode, the cruciate ligaments are the foundation of knee joint kinematics. Together with the bony confines of the condyles they not only determine the type of motion that will occur, but also provide stability from outside forces, preventing subluxation during the range of motion. Human knee motion does not occur as a simple hinged model, but rather combines gliding, sliding and rotation. To accomplish this, the anterior and posterior cruciate ligament function according to the principles of a crossed four bar linkage. Considering the knee in a single plane, the movement of the anterior cruciate and posterior cruciate ligament origins and insertions define circular arcs during flexion and extension according to the principles of a crossed four bar linkage. This four bar linkage is closely related to and dependent upon the bony constraints of the surfaces of the tibia and femur. It is for this reason that the anatomic origin and insertion of both the anterior cruciate ligament and posterior cruciate ligament is so crucial. Any attempt at reconstructing the anterior and posterior cruciate ligament must consider these points of the four bar linkage system if successful reconstruction is to be obtained. Of the four points on the crossed four bar linkage system, the femoral origins are the most crucial. If anterior cruciate or posterior cruciate ligament reconstruction is performed in the appropriate location, then normal motion and stability can be reconstructed. If, however, these points are deviated from in reconstruction, either the ligament will be too loose to function in an anatomic fashion or too tight to allow normal motion. If the latter occurs, as normal range of motion is regained, the ligament substitute will ultimately fail. This invention facilitates the determination of the isometric cruciate ligament points of femoral origin for anterior and posterior cruciate ligament reconstruction.
Osteotomy of the upper part of the tibia is described beginning on page 30 in an article by Mark B. Coventry, M.D. published in "The Journal Of Bone And Joint Surgery" in Vol. 55-A, No. 1, January 1973, which is incorporated herein by reference. As illustrated in FIG. 7-B on page 33 of Coventry, the osteotomy of the upper part of the tibia is done to remove a wedge of the tibia, which is then closed and retained in place by a stepped staple.